With the development of semiconductor technology and the miniaturization in the feature size of device, the requirements on accuracy and stability during the production process are increasingly strict, even a deviation of a few nanometers can cause the yield loss. Especially, the feature sizes of polysilicon gates and circular contact holes are more sensitive. Circular uniformity is one of the technical parameters of the circular contact holes in the technical standard, its importance becomes higher and higher in the process whose feature size is 65 nanometers, even 45 nanometers and below.
During the process whose feature size is 45 nanometers and below, the accuracy problem of the feature size may indirectly cause that the semiconductor device performance deviates from the normal values, for example it might cause an electric leakage, etc. In some more serious situation, it can even result to the device failure, for example, short-circuit will be caused by the too small distance between contact holes. In the existing technology, the sampling method is applied to measure the circular uniformity of the circular contact holes. A certain percentage of contact holes are randomly selected in various locations of the wafer according to the shapes and sizes of the contact holes, and average values of the partial measurement are used to represent the overall measuring values of the circular uniformity of the contact holes on the wafer.
The measure method with partial elected points and random sampling usually causes sampling bias, thus it can not reflect the technical level of the contact holes comprehensively. Firstly, in the process of forming the contact holes, the influence due to the impurity during the exposure, etching and cleaning steps, which causes single or accidental substandard circular contact holes, can not be surely detected. The measured contact holes which are up-to-standard do not mean all the contact holes are up-to-standard. Secondly, in the regions where the contact holes are dense, since the distance between the contact holes is short, the requirements on the accuracy of the circular uniformity are relatively high. Therefore, the random sampling method cannot guarantee the weakest position in the art can be measured.
Chinese patent (CN102157496A) discloses a contact hole test device and a method for testing leakage current of grid by active area contact hole, wherein a plurality of parallel belt-shaped active areas are arranged in length direction; multi-line and two rows of active area contact holes are respectively generated at two sides of each active area; a first metal wire passing through the top end is connected to be an active area contact hole link from the first line and second row of the active area contact holes to the last line and last second row of the active area contact holes; grid electrodes with a length greater than the width of the active area are disposed on gate oxide surfaces on the active areas between two rows of active area contact holes; two ends of the grid electrode are respectively provided with grid electrode contact holes; a second metal wire passing through the top end is connected to be a grid electrode link from the first line and second row of the grid electrode contact holes to the last line and last second row of the grid electrode contact holes. The testing device and method can truly reflect the defects possibly occurring in the manufacturing procedure of MOSFET (metal-oxide-semiconductor field effect transistor) devices.
Chinese patent (CN102376601A) discloses a detection method and structure for deviation of a contact hole. The detection method comprises the following steps of: providing a wafer and at least forming two groups of detection graphs which are in parallel to a plane coordinate axis and are orthogonally arrayed on a semiconductor substrate in a detection region, wherein the detection graphs comprise first graphs and second graphs which are arranged at intervals along the array direction of the detection graphs, the conducting property of a first graph is different from that of a second graph; a first space is reserved between adjacent first graphs; carrying out a production process of the contact hole and respectively forming contact holes arranged along the direction of the coordinate axis on each detection graph and enabling a second space reserved between adjacent contact holes to be different from the first space; scanning the surface of the wafer by adopting an electron beam and acquiring the scanning brightness of the position of each contact hole on the surface of the wafer; and judging the partial deviation direction and the amplitude of the contact hole according to the scanning brightness of the position of each contact hole. According to the detection method and structure provided by the invention, the deviation direction and the amplitude of the contact hole on the wafer can be accurately detected.